1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to disk drives in which the motion of the actuator assembly is damped using a damping magnet placed within the magnetic field of the voice coil motor.
2. Description of the Prior Art
A typical hard disk drive includes a head disk assembly (xe2x80x9cHDAxe2x80x9d) and a printed circuit board assembly (xe2x80x9cPCBAxe2x80x9d). The HDA includes at least one magnetic disk (xe2x80x9cdiskxe2x80x9d), a spindle motor for rotating the disk, and a head stack assembly (xe2x80x9cHSAxe2x80x9d) that includes a head with at least one transducer for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (xe2x80x9cHGAxe2x80x9d) that extends from the actuator assembly and biases the head toward the disk; and (3) a flex cable assembly: that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function that provides a xe2x80x9cgram loadxe2x80x9d biasing force and a hinge function that permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that carries the head and transmits the gram load biasing force to the head to xe2x80x9cloadxe2x80x9d the head against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be xe2x80x9cflyingxe2x80x9d over the disk when in this state.
Within the HDA, the spindle motor rotates the disk or disks, which are the media to and from which the data signals are transmitted via the head on the gimbal attached to the load beam. The transfer rate of the data signals is a function of rotational speed of the spindle motor; the faster the rotational speed, the higher the transfer rate. A spindle motor is essentially an electro-magnetic device in which the electromagnetic poles of a stator are switched on and off in a given sequence to drive a hub or a shaft in rotation.
FIG. 1 shows the principal components of a magnetic disk drive 100 constructed in accordance with the prior art. With reference to FIG. 1, the disk drive 100 is an Integrated Drive Electronics (IDE) drive comprising a RDA 144 and a PCBA 114. The HDA 144 includes a base 116 and a cover 117 attached to the base 116 that collectively house a disk stack 123 that includes a plurality of magnetic disks (of which only a first disk 111 and a second disk 112 are shown in FIG. 1), a spindle motor 113 attached to the base 116 for rotating the disk stack 123, an HSA 120, and a pivot bearing cartridge 184 (such as a stainless steel pivot bearing cartridge, for example) that rotatably supports the HSA 120 on the base 116. The spindle motor 113 rotates the disk stack 123 at a constant angular velocity. The HSA 120 comprises a swing-type or rotary actuator assembly 130, at least one HGA 110, and a flex circuit cable assembly 180. The rotary actuator assembly 130 includes a body portion 140, at least one actuator arm 160 cantilevered from the body portion 140, and a coil portion 150 cantilevered from the body portion 140 in an opposite direction from the actuator arm 160. The actuator arm 160 supports the HGA 110 with a head. The flex cable assembly 180 includes a flex circuit cable and a flex clamp 159. The HSA 120 is pivotally secured to the base 116 via the pivot-bearing cartridge 184 so that the head at the distal end of the HGA 110 may be moved over a recording surface of the disks 111, 112. The pivot-bearing cartridge 184 enables the HSA 120 to pivot about a pivot axis, shown in FIG. 1 at reference numeral 182. The storage capacity of the HDA 111 may be increased by including additional disks in the disk stack 123 and by an HSA 120 having a vertical stack of HGAs 110 supported by multiple actuator arms 160.
The xe2x80x9crotaryxe2x80x9d or xe2x80x9cswing-typexe2x80x9d actuator assembly comprises a body portion 140 that rotates on the pivot bearing 184 cartridge between limited positions, a coil portion 150 that extends from one side of the body portion 140 to interact with one or more permanent magnets 192 mounted to back irons 170, 172 to form a voice coil motor (VCM), and an actuator arm 160 that extends from an opposite side of the body portion 140 to support the HGA 110. The VCM causes the HSA 120 to pivot about the actuator pivot axis 182 to cause the read write heads of the HSA 120 to sweep radially over the disk(s) 111, 112.
Dynamic load/unload (LUL) of flying heads in rigid disk drives offers many technical advantages along with new engineering challenges. Among these challenges are 1) methods of retaining the actuator in the non-operational position on the ramp and 2) ensuring that upon loss of power, the flying heads are not unloaded at too high of a velocity.
Many solutions for retaining the actuator in the non-operational position on a contact-start-stop (CSS) drive are well known such as magnetic, air-vane, spring detent, and the like. Furthermore, the contact friction of the heads resting on the CSS area (an annular region on each of the disks 111, 112 that is typically located at the inner diameter -ID) of the disks of a CSS drive helps retain the actuator assembly 120 in the non-operational position. These solutions work quite well to retain the actuator assembly 120 in the non-operational position during mechanical shocks. Controlled, low-velocity unloads are required to ensure that neither the heads nor media are damaged. The critical unload operation occurs when power is suddenly removed from the drive. The actuator may be moving at a high velocity towards the ramp; neither normal servo control nor full power is available to brake the actuator assembly 120 before loading onto the ramp. In this case, some means of slowing the actuator prior to reaching the ramp would aid in unload velocity control.
For dynamic LUL drives, a controlled, low-velocity loading of the heads onto the rotating disks is necessary to eliminate the potential of head/media contact and damage during the load. In a LUL drive, portions of the head suspension contact a ramp during non-operation, and the friction between the ramp and suspension are designed to low values to allow low-velocity motion control. This low friction offers little retaining force to the actuator and may allow the actuator to move under the influence of even small mechanical shocks. A detent on the ramp is usually employed to increase the retaining force, but the angle of detent is similarly limited to low values and hence offers little improvement.
What are needed, therefore, are improved head stack assemblies and drives that include a structure to slow the actuator prior to reaching the ramp or the CSS area of the disk or disks.
Accordingly, this invention may be regarded as a disk drive including a disk having a recording surface, a ramp structure defining a ramp surface and a head stack assembly. The head stack assembly includes an actuator body, an actuator arm cantilevered from the actuator body and including a head for reading and writing on the recording surface, the head resting on the ramp surface when the disk drive is non-operational, a coil cantilevered from the actuator body in an opposite direction from the actuator arm, the coil defining a first leg and a second leg and a damping magnet disposed between the first leg and the second leg. The damping magnet may be configured to exert a damping force on the head stack assembly, the damping force being greater when the head is on the ramp surface than when the head is over the recording surface.
The disk drive may further include a first and a second VCM magnet. The first VCM magnet may define a first south magnetic pole and a first north magnetic pole separated by a first transition zone. The second VCM magnet may face and be spaced apart from the first VCM magnet, the second VCM magnet defining a second south magnetic pole and a second north magnetic pole separated by a second transition zone, the second transition zone being aligned with the first transition zone. The region of highest magnetic flux density of the damping magnet may be substantially aligned with the first and second transition zones when the head rests on the ramp surface. The coil may be partially encased in a plastic overmold and the plastic overmold may be configured to secure the damping magnet between the first and second legs.
The present invention is also a head stack assembly for a disk drive including a disk having a recording surface. The head stack assembly includes an actuator body, an actuator arm cantilevered from the actuator body and including a head configured for reading and writing on the recording surface of the disk, a coil cantilevered from the actuator body in an opposite direction from the actuator arm, the coil defining a first leg and a second leg, and a damping magnet disposed between the first leg and the second leg for exerting a damping force on the head stack assembly. The damping force may be greatest when the head is positioned at a predetermined non-operational position in the disk drive.
The coil may be partially encased in a plastic overmold and the plastic overmold may be configured to secure the damping magnet between the first and second legs. The predetermined non-operational position may be located on a contact start stop (CSS) area of the disk. The selected non-operational position may be located on a ramp surface of a ramp load structure of the disk drive on which the head rests when the disk drive is non-operational.
The present invention may also be viewed as a disk drive that includes a disk having a recording surface and a head stack assembly. The head stack assembly includes an actuator body, an actuator arm cantilevered from the actuator body and including a head for reading and writing on the recording surface, a coil cantilevered from the actuator body in an opposite direction from the actuator arm, the coil defining a first leg and a second leg, and a damping magnet disposed between the first leg and the second leg. The damping magnet may be configured to exert a damping force on the head stack assembly, the damping force being greater when the head is at a predetermined non-operational position than when the head is over the recording surface.
The disk drive may further include a first VCM magnet and a second VCM magnet. The first VCM magnet may define a first south magnetic pole and a first north magnetic pole separated by a first transition zone. The second VCM magnet may face and be spaced apart from the first VCM magnet, the second VCM magnet defining a second south magnetic pole and a second north magnetic pole separated by a second transition zone, the second transition zone being aligned with the first transition zone, a region of highest magnetic flux density of the damping magnet being substantially aligned with the first and second transition zones when the head is at the predetermined non-operational position. The coil may be partially encased in a plastic overmold and the plastic overmold may be configured to secure the damping magnet between the first and second legs. The disk may further include a contact start stop (CSS) surface and the predetermined position may be located on the CSS surface. The disk drive further may include a ramp structure defining a ramp surface and the predetermined position may be located on the ramp surface.
The foregoing and other features of the invention are described in detail below and set forth in the appended claims.